The present invention relates to sonar systems, and more particularly, to a sonar system which has an improved probability of detecting moving targets by cancelling all stationary targets within the search area.
There is a need to assist water-side security of harbors, inlets and offshore structures through detection of underwater intruders. Such intruders are often relatively small in size and include human swimmers, swimmer delivery vehicles, miniature submarines, bottom-crawlers, remotely piloted underwater vehicles and self-propelled mines. A significant problem arises if one attempts to use a conventional sonar system to detect such underwater intruders in harbors and inlets, and adjacent offshore structures. Stationary echo returns in such security sensitive areas often mask the intruders. In other words, the presence of the intruders cannot be reliably detected by a conventional sonar system because the echo returns therefrom are overpowered or dominated by echo returns from stationary submerged objects prevalent in such security sensitive areas. These objects include piers, pilings, buoys, pipelines, submerged portions of surface vessels, etc. Fluctuations in environmental conditions, such as water temperature gradients, further inhibit the ability of conventional sonar systems to detect small moving underwater objects in such security sensitive areas.